Within the IP (Internet Protocol) Multimedia Subsystem (IMS) as defined by 3rd Generation Partnership Project (3GPP) Session Initiation Protocol (SIP) defined by Internet Engineering Task Force (IETF) is used for controlling communication. SIP is an application-layer control protocol for creating, modifying, and terminating sessions with one or more participants. These sessions may include Internet multimedia conferences, Internet telephone calls, and multimedia distribution. Members in a session can communicate via multicast or via a mesh of unicast relations, or a combination of these.
Different types network entities and functions exist in the IMS network. Call Session Control Functions (CSCF) implement a session control function in SIP layer. The CSCF can act as Proxy CSCF (P-CSCF), Serving CSCF (S-CSCF) or Interrogating CSCF (I-CSCF). The P-CSCF is the first contact point for the User Equipment (UE) within the IMS; the S-CSCF actually handles the session states in the network; the I-CSCF is mainly the contact point within an operator's network for all IMS connections destined to a subscriber of that network operator, or a roaming subscriber currently located within that network operator's service area.
The functions performed by the I-CSCF are, for example, assigning an S-CSCF to a user performing SIP registration and routing SIP requests received from another network towards the S-CSCF. The S-CSCF performs the session control services for the UE. It maintains a session state as needed by the network operator for support of the services and may be acting as Registrar, i.e. it accepts registration requests and makes its information available through the location server (e.g. HSS). The S-CSCF is the central point to users that are hosted by this S-CSCF. The S-CSCF provides services to registered and unregistered users when it is assigned to these users. This assignment is stored in the Home Subscriber Server (HSS).
An Application Server (AS) is offering value added IP multimedia (IM) services to users of the IMS network and resides either in the IMS user's home network or in a third party location. The third party could be a network or simply a stand-alone AS. The AS may host and execute various services and can influence and impact a SIP session on behalf of the services. The IP multimedia Subsystem Service Control Interface (ISC) interface is between the S-CSCF and the service platforms (i.e. Ass). The ISC interface offers extended services to subscribers. ASs that are connected to the IMS are controlled via ISC interface. The protocol used on the ISC interface is the SIP.
A media gateway control function (MGCF) acts as an interworking point between a circuit switched (CS) network and an IP network in the control plane of the network. The MGCF controls the parts of the call state related to connection control for media channels in a media gateway (MGW), communicates with call state control, and performs protocol conversion between the call control protocols, such as SIP and ISUP.
Telephony Application Server (TAS) is a SIP-AS providing the network support for multimedia telephony services. Such services may include call forwarding, call transfer, conference call, call hold and other well known services from traditional circuit switched telephone networks.
The 3GPP is specifying multimedia session continuity (MMSC) which defines procedures for session continuity using SIP mechanisms. The MMSC is to include procedures where the UE moves from first access technology to second access technology, e.g. from wireless local area network (WLAN) to universal terrestrial radio access network (UTRAN), and the complete SIP session or part of the media components in the session continues seamlessly in the new access. Similar procedures should work also conjunction with voice call continuity (VCC), i.e. where the voice session is transferred from/to CS domain using VCC, but the SIP session is transferred using MMSC procedures. Also it should cover procedures where the sessions or media components in the session are transferred between multiple devices.
A session split/merge application server (AS) is a network entity responsible to represent a single SIP session towards the other end, even if the UE needs to use separate sessions in his end. The split/merge AS is also responsible to split and merge the session on fly in middle of the access transfer procedure. For example, if the UE is engaged in a SIP session in WLAN that includes voice over IP (VoIP) speech component and video sharing media, and the UE then moves from WLAN access to UTRAN access where VoIP is not possible or preferred, the UE should perform VCC procedure for the speech media, in order to transfer the speech to CS over UTRAN and transfer the video sharing SIP session to packet switched (PS) over UTRAN. The role of the split/merge AS in this scenario is to combine the speech and video sharing sessions after the access transfer and hide the session split from the UE in the other end. In other words, the UE in the other end may receive media updates (e.g. SIP re-INVITE requests) due to the access transfer, but the other end should not realize that the session has been split into two due to access transfer.
The split/merge AS should merge together the speech sessions it receives via MGCF, and SIP sessions it receives via P-CSCF, S-CSCF and present them as a single session towards the other end. The problem is that the split/merge AS should not merge the sessions that belong to different services. Otherwise the network is not able to route the sessions correctly to proper servers.
The object of the invention is to overcome the above problems.